1. Field of the Invention
The present invention generally relates to a method of and an apparatus for analyzing a circuit, and more particularly, to a method of and apparatus for analyzing the transmission characteristics of a circuit apparatus such as an electric circuit, an electronic circuit, and an integrated circuit.
2. Description of the Related Art
Recently, the data transmission speed of an image processing apparatus and a communication apparatus, for example, is increasing even to more that 1 GHz. In the case of such a high frequency signal, the transmission characteristics of a signal may be considerably different from that of a low frequency signals. For example, if a transmission channel has a perpendicular corner, current density at the inside of the corner becomes greater than that of the outside of the corner. In addition, since a reflection factor increases, current loss also increases. In such a case, if the signal integrity of the circuit apparatus is not verified, the circuit apparatus may fail to transmit data normally. Accordingly, it is important to verify the signal integrity by analyzing the transmission characteristics using simulation.
The signal integrity of a circuit apparatus can be verified as follows. Three dimensional data of the circuit apparatus such as an electronic circuit board is generated. The 3 dimensional data includes transmission wirings, insulative layers surrounding the transmission wirings, and conductive layers such as a power supply layer and a ground layer. From the 3 dimensional data, 2 or 3 dimensional mesh is generated thereby to divide the circuit apparatus with the generated mesh. As a result, the circuit apparatus is made discrete. Electromagnetic analysis method is applied to each unit of mesh so as to obtain electric property parameters such as a “S” parameter of the transmission wiring.
Conventionally, two methods have been employed for obtaining the electric property parameters of the circuit apparatus. According to a first method, the entire circuit apparatus is covered with a uniformly generated mesh for performing the electromagnetic analysis for each unit of the mesh. According to a second method, the circuit apparatus is first divided into multiple portions, and each portion of the circuit apparatus is covered with a mesh generated for each portion for performing the electromagnetic analysis.
Japanese Laid-Open Patent Applications No. 2002-288241, No. 7-302277, and No. 7-302258 disclose inventions relevant to the related art.
However, according to the first method described above, the uniformly generated mesh covers such region of the insulative layer that no transmission wiring is formed therein and such region of the power supply layer and ground layer that are not adjacent to the transmission wiring. The problem is that a long time is required for generating the mesh and analyzing the electromagnetic field in such regions.
According to the second method described above, the time required for generating the mesh and analyzing the electromagnetic field in the circuit apparatus can be reduced since the multiple portions of the circuit apparatus can be processed concurrently. However, the problem is that the 3 dimensional data needs to be modified for dividing the circuit apparatus into multiple portions, and the electric property parameters obtained as a result of the electromagnetic analysis need to be combined.